1. Technical Field
This invention relates to a mechanism for positioning a ribbon in a printing machine.
2. Background Art
In most types of printing machines, ribbon shifting, either to change colors or to make corrections, is accomplished by one of two methods. In the first method, illustrated in U.S. Pat. No. 3,451,520, issued on June 24, 1969, to the assignee of this invention, the ribbon is supported in a guide, such as a bail arm, which is mechanically arranged to align the desired band on the ribbon with a printing element in a printing station. Although this method is satisfactory when only two colors are employed, excessive vertical movement of a multi-colored ribbon within the guide can cause snagging and dragging. Furthermore, this method is not particularly suited for high-speed printing in which it may be desirable to change print colors every character, or even every column in a matrix-formed character.
In the second method, illustrated in U.S. Pat. No. 4,329,072, issued May 11, 1982, to the assignee of this invention, a ribbon cartridge is supported on a pivotable plate which is rotated by a stepper motor to align different color bands with the print element. While this method has overcome some of the drawbacks present in the first method, it is still not conducive to rapid color changes, especially when printing in more than two colors is desired. When the entire ribbon cartridge and its supporting plate has to be rotated to effect a color change, it is practically impossible to change colors within a character, or every character, without slowing the printing speed to an unacceptable level.